Spinal stenosis, a narrowing of the spinal canal, may result in pain, numbness, and muscle weakness in the limbs. The condition affects elderly people primarily and is caused by degenerative changes in the body that cause enlargement of the facet joints and thickening of the ligaments resulting in constriction of the spinal cord and nerves. Such constriction may be relieved by surgical intervention such as a spinal decompression procedure.
Spinal decompression surgery may be performed anywhere along the spine to remove any structures that are compressing the nerves in the spinal canal or vertebral foramen (opening through which the spinal cord passes). Lamina, the bone that forms the backside of the spinal canal, may be removed along with other soft tissues to allow for more room for the nerves. The laminae are a part of the posterior arch of the vertebrae. The laminae comprise two flattened plates that extend medially from the pedicles and meet at the spinous process to form the posterior wall of the spinal foramen. Depending on the extent of stenosis, one of a variety of decompression surgeries may be performed including laminectomy, laminotomy, foraminotomy, or laminaplasty. Spinal fusion, a surgical technique used to join two or more vertebrae, is another surgical intervention option that is often performed in combination with such decompression procedures to immobilize the affected vertebrae and stabilize sections of the spine. Fusion may use a combination of bone graft(s), rods and screws to connect to vertebrae together, thereby inducing bony incorporation and healing the vertebrae together as one piece of bone. Fusion helps prevent recurrence of spinal stenosis and aids in eliminating pain arising from an unstable spine. Supplementary bone tissue (e.g., autologous iliac crest bone, allograft tissue, synthetic cage with bone substitute filler) is used in conjunction with the body's natural bone growth processes to fuse the vertebrae. However, autologous tissue recovery often leads to graft site morbidity. Furthermore, fusion often leads to adjacent segment disease, which may limit the duration of success of the operation. Thus, there remains a need for safe, effective grafts as well as methods for treating the spine after surgical intervention for conditions such as spinal stenosis.